“It’s like a Hitchcock movie,” says his wife, Marty, referring to “The Birds,” a 1963 horror film in which birds gather in huge flocks and attack humans. But these birds, according to Marty, are descending upon farm fields and preying upon the remnants of the autumn harvest. She first saw these gleaners on Jan. 4.

If their intent is to intrigue the populace, they have come to the right place. John DeMarrais, who lives near the Quakertown firehouse, has been a birdwatcher for 60 years and has served on the board of N.J. Audubon Society for 30 years.

Fascinated by this “interesting phenomenon,” DeMarrais puts the flock at about 30,000 to 50,000, but concedes “it’s very hard to estimate huge groups of birds; very, very hard. You have to do the best you can.”

He says the birds are lingering this far north because there is no snow cover to interfere with their dining. “Once we get 4 to 5 inches of snow, they’ll move south and then they’ll be gone,” he says.

Meanwhile they could make people “somewhat apprehensive.” The birds appear suddenly and they make “a continuous din, sort of a rattling noise… they move quickly; they are skitzy and jumpy.” But, DeMarrais says, they are harmless.

He suspects that the thousands of grackles that pass through his neighborhood in the mornings and before dusk are merely the grackle contingent of a much larger flock that roosts each night possibly somewhere around Ringoes. He says that historically there has been a roosting site in that area. He said these birds travel in huge mixed flocks that include red-wing blackbirds, cowbirds and starlings.

In the mornings the grackles — “only a small fraction of the roost” — commute north to feed in the fields of northern Hunterdon or possibly in the Lehigh Valley, and then return to the roosting area in the evening, he believes. The other species might head off in other directions.

“That means I’ve got to go and try to find the roost, which is going to be hard. That means following them maybe at night. I’m committed to doing it. It’s sort of an interesting ornithological event. It’s just something that you’re very curious about. To see how many birds are in the roost, how they roost, and that sort of thing.”

A retired hospital administrator, DeMarrais has a schedule into which such a quest might fit.